EXCHANGE 



1 EXL1BRIS 




BIOLOGY 
LIBRARY 



A CONTRIBUTION TO THE KNOWLEDGE OF 

THE INTERNAL ANATOMY OF 

TRICHOPTERA 



A Thesis 

Presented to the Faculty of the Graduate School of 

Cornell University for the degree of 

Doctor of Philosophy 






By 



HAZEL ELISABETH BRANCH 



Reprinted from the Annals of the Entomological Society of America 
Vol. XV, pp. 256-280 

Columbus, Ohio: September, 1922 



A CONTRIBUTION TO THE KNOWLEDGE OF 

THE INTERNAL ANATOMY OF 

TRICHOPTERA 



A Thesis 

Presented to the Faculty of the Graduate School of 

Cornell University for the degree of 

Doctor of Philosophy 



By 
HAZEL ELISABETH BRANCH 



Jfc 



Reprinted from the Annals of the Entomological Society of America 
Vol. XV, pp. 256-280 

Columbus, Ohio: September, 1922 




BIOLOGY 
LIBRARY 



A CONTRIBUTION TO THE KNOWLEDGE OF THE 
INTERNAL ANATOMY OF TRICHOPTERA.* 

By HAZEL ELISABETH BRANCH, 
Wichita, Kansas. 

NERVOUS SYSTEM. f 

The nervous system of the trichopterous larvas is comparatively 
primitive and agrees with that of the lepidopterous larvas in the number 
of pairs of ganglia and also resembles, in some respects, the arrangement 
in relation to the body segments. Exclusive of the ganglia in the head, 
which are normal in number and position, there are three pairs for the 
thorax and eight pairs for the nine abdominal segments, the seventh 
abdominal segment being the most posterior in which ganglia are found. 

In the head of Limnophilus indimsus the supra-cesophageal ganglia 
are situated with their anterior margin on a line immediately posterior 
to the eyes. The combined width of the ganglia is about one-half that 
of the head. Each ganglion gives off laterally and in a forward direc- 
tion, an optic nerve which branches to supply each of the simple eyes 
of the visual area. In front of the junction of the two ganglia is the 
frontal ganglion, small and shield shaped, connected to the supra- 
cesophageal ganglia by a pair of arms. Proceeding from each arm of the 
frontal ganglion, close to its attachment with the supra-cesophageal 
ganglion, is a nerve which extends forward and sends an outer branch to 
the labrum, and an inner branch to the dorsal region of the buccal 
cavity, see Plate XIV, Figs. 4 and 5, at lb x and b. Between the point 
of attachment of the arm of the frontal ganglion with the supra-cesoph- 
ageal ganglion, and the optic lobe, (opt), is the slender antennal nerve 
rising from the anterior margin of the ganglion and possessing a fellow 
in like position upon the other ganglion, see Plate XIV, Figs. 4 and 5 
at ant. Upon its posterior face, each ganglion gives rise to a pro- 
tuberance from which issues a nerve that converges toward its fellow 
and meets it upon a median line. At this union a small 
ganglion is formed and to this are also joined, the nerves 
coming from the sympathetic ganglia. These sympathetic ganglia are 
single, one upon each side of the oesophagus and possessing a nerve 
connection with the posterior protuberance of the supra-cesophageal 
ganglion of its respective side, See Plate XIV, Figs. 4 and 5. 

The recurrent nerve of the frontal ganglion extends in a posterior 
direction between the supra-cesophageal ganglia and the oesophagus 

* A contribution from the Department of Entomology, Cornell University, 
prepared under the supervision of Dr. O. A. Johannsen, to whom and also to Dr. 
J. G. Needham and Dr. J. T. Lloyd, I wish to express my gratitude for the valuable 
assistance rendered. 

t In gross dissection, hot water killing and Gilson's fixing solution were found 
to be most advantageous. 



2o6 






1922] Branch: Internal Anatomy of Trichoptera 257 

and fuses with the nerve which extends posteriorly from the ganglion 
situated at union of the nerves from the posterior protuberances of the 
supra-cesophageal ganglia and the sympathetic ganglia of each side. 

From the ventral face of the supra-cesophageal ganglia, arises a 
pair of connectives, the crura cerebri, which connect the supra-cesoph- 
ageal ganglia with the sub-cesophageal ganglion. 

Immediately in front of the union of the crura cerebri with the 
supra-cesophageal ganglia, the cesophageal ring of the tritocerebrum 
arises. This is a loop w r hich encircles the oesophagus and has its ends 
connected with the supra-cesophageal ganglia, see Plate XIV, Fig. 5 at or. 
The supra-cesophageal ganglia does not fit closely upon the oesophagus 
normally, but leaves some space laterally and ventrally for the expan- 
sion of the tube in feeding. Faivre 1857, states that the supra-cesoph- 
ageal ganglia possess the seat of motive power and will power and Binet, 
1894, strengthens this statement by the results of his own experiments 
which show that an insect will live for months with the supra- 
cesophageal ganglia removed but will not eat unless the food is placed 
in its mouth as it has no power to move toward the food. 

The sub-cesophageal ganglion is situated slightly back of the 
posterior margin of the supra-oesophageal and below the oesophagus 
but well within the limits of the head cavity. This ganglion gives off 
three pairs of nerves, the most ectal and dorsal of which extends in a 
forward and upward direction and, upon a level with and in front of the 
frontal ganglion, branches. One branch extends to the base of the 
labrum, see Plate XIV, Figs. 5 and 6 at Ib2, while a second branch 
extends to the dorsal side of the mandible, see Plate XIV, Figs. 5 and 6 
at md2. The second pair of nerves from the sub-cesophageal ganglion 
arises ventrad of the first pair and extends forward also branching. 
The ectal branch of each nerve reaches the musculature of the maxilla, 
mxl ; and an ental branch divides and one part goes to the maxillary 
sclerite and the other to the labium, see Plate XIV, Figs. 5 and 6, at mx2 
and H2. This pair is connected by a nerve just below the frontal ganglion, 
and the cross nerve bears a small median ganglion. The third pair of 
nerves is ventrad of the second pair and extends forward directly to the 
labium, which it innervates, lil. 

The above description is made from several dozen specimens of the 
species Limnophilus indimsus Walker. The head ganglia of the other 
species studied do not vary materially. 

Posteriorly the sub-cesophageal ganglion gives off a pair of com- 
missures which connect to the first thoracic* ganglion lying in the 
prothorax. In the thorax and abdomen there is much variation among 
the species as to the relation of the ganglia to their respective seg- 
ments. Upon observation of these three species (Limnophilus indivisus 
Walker, Hydropsy diodes anal is Banks and Phryganea interrupta Say,) 
two centers of fusion will be found, one in the thorax and one in the 
abdomen at the posterior end of the chain. As above stated, there are 
three thoracic and eight abdominal ganglia. The prothoracic and 

* Each ganglion of the thorax and abdomen is a pair of fused ganglia. 



5077.13 



258 Annals Entomological Society of America [Vol. XV, 

mesothoracic ganglia are about the same size as the sub-cesophageal 
ganglion and are each situated equidistantly from the anterior and 
posterior margins of the segments and this condition prevails for the 
three species. The meta thoracic ganglion is larger than those of the 
preceding segments and its position is not the same in the different 
species for it is here that the thoracic fusion point occurs. In Phryganea 
interrupta the ganglion is centrally located with the ganglion of the 
first abdominal segment just within the posterior border of the meta- 
thorax. In Limnophilus indivisus, the metathoracic ganglion has 
migrated forward and the first abdominal ganglion has followed until 
the latter occupies the central position with the metathoracic ganglion 
well in the front half of the segment. In Hydropsychodes analis, the 
condition is the same as in L. indivisus. 

In the abdomen of the three species the positions of the ganglia 
are more noticeably variable. In P. interrupta the first abdominal 
segment bears at its posterior margin, the ganglion of segment two 
and segment two is void of any ganglion, but receiving its innervation 
from its respective ganglion located in segment one. The ganglia of 
segments three, four, five and six occur in their respective segments 
near the front margins. Segment seven bears in its front half, two 
ganglia; these are the ganglia for segments seven and eight and they 
are very closely united, but not fused at all, Plate XIV, Fig. 2. In 
L. indivisus, the ganglion of segment two occupies a central position 
in segment one, indicating a forward migration. Segments three, four 
and five have their ganglia in the front half of the segment as in P. 
interrupta. In segment six all the ganglia of the three segments, six, 
seven and eight, are placed; those relating to segments seven and eight 
are closely united, practically fused, and take a position in the posterior 
half of the segment. The ganglion for segment six is in the anterior 
half of the segment, Plate XIV, Fig. 1. In H. analis we find an arrange- 
ment in the abdomen which varies from that which Pictet, 1834, 
observed in Hy dropsy che, for he saw all the ganglia here upon the 
divisions between the segments. In this particular species, the ganglion 
for segment two is in segment one as usual, and the ganglion for segment 
three is on the margin between segments two and three which is a 
forward migration. The ganglion for segment four is in front of the 
center of the segment and the ganglion for segment five is back of the 
center of its respective segment. In the sixth abdominal segment 
are three ganglia, for segments six, seven and eight respectively and all 
are in a line and practically fused, Plate XIV, Fig. 3. 

The thoracic ganglia and the abdominal from one to six innervate 
their respective _segments and appendages, the seventh abdominal 
appears to have only one pair of nerves which extend backward into 
segment seven, the eighth abdominal ganglion innervates segment 
eight and nine, as well as the swimmerets. which extend out from seg- 
ment nine. There are various ways for the eighth abdominal segment 
to innervate segment nine. In P. interrupta and H. analis it sends a 
nerve directly to the segment, but in L. indivisus the nerve which 
extends to segment eight branches and sends a branch to segment 



1922] Branch: Internal Anatomy of Trichoptera 259 

nine, this arrangement leaves one less pair of nerves arising from ganglion 
eight in L. indivisus than in P. interrupta or H. analis. 

Upon a comparison of the three Figures, Nos. 1, 2 and 3, Plate XIV, 
a sequence of fusion is evident. This sequence places P. interrupta 
as the most generalized and H. analis as the most specialized and L. 
indi-dsiis as intermediate. Vorhies, 1905, has described the nervous 
system of Platyphylax designatus Walker and it falls between P. 
interrupta and L. indivisus for the ganglia of the seventh and eighth 
segments have migrated so that the ganglion for segment seven is just 
inside the posterior margin of segment six and the ganglion for segment 
eight remains in segment seven, but very close to its anterior margin. 
Betten, 1901, in his description of Molanna cinerea does not show it 
to vary from P. designatus. Pictet, 1834, figures Phryganea striata 
Fab. to fall between P. designatus and L. indimsus with the ganglia 
for segments six, seven and eight in segment six, but ganglia seven 
and eight not fused. Klapalek, 1888, does not note any variation of 
position, but merely gives the number of ganglia and their general 
distribution. 

From the above it seems reasonable to think that the nervous system 
of the order will reveal grades of consolidation of the ganglia which may 
have a decided bearing upon classification. 

REPRODUCTIVE SYSTEM. 

The writer has done very little in this system beyond the mere 
location of the organs, for the matter seems to have been given adequate 
attention by Zander, 1901, Lubben, 1907, and Marshall, 1907. As 
to the period of the appearance of the organs there is a difference of 
opinion. Pictet, 1834, Klapalek, 1888, and Vorhies, 1905, make the 
statement that the organs do not appear until near the period of pupa- 
tion or at least in a very old larva; Lubben, 1907, discusses conditions 
in a transforming larva, while Marshall, 1907, speaks of the condition 
of the organs in the youngest larva he had, but does not give the stage. 
In all the specimens observed by the writer, the gonads appear in 
the early forms, showing clearly both in gross dissection and sections. 
In P. interrupta taken in October and H analis taken in late December 
from under the ice in streams, the gonads are distinct and developed 
far enough' so that tubules may be seen, Plate XIV, Fig. 7. This period 
is long before there are any signs of pupation either in case or larva. 

Within the species two shapes of gonads appear. In P. interrupta 
some are elongate and flat, while others are spherical. This seems to 
point to a sex differentiation, the elongate one probably destined to 
become female organs and the spherical ones male organs, Plate XIV, 
Fig. 2. In gross dissection in L. indivisiis only one kind of a gonad 
was observed, this circular and plate-like of five pairs of tubules. Plate 
XIV, Fig. 1, at gd. In each gonad there are two outgrowths or attach- 
ments; one from the outer side and extending to the ventral body wall 
of the second abdominal segment and resembling a supporting thread 
or tissue, the inner side outgrowth appears as a duct and the tubules 
of the gonad may be seen converging toward the head of this duct. 




260 Annals Entomological Society of America [Vol. XV, 

The duct .extends in a posterior direction and extends to the ventral 
side of the eighth segment, where it is lost. Lubben, 1907, shows that 
these ducts pass into external, sculptured plates in the eighth segment 
but I have been unable to find any such structure or any opening what- 
ever at this point on any of the specimens. In H. analis the gonad 
is oval, but appears spherical in frontal section as the long axis of the 
gonad is at right angles to that of the body of the larva. The gonads 
of the above three species are in pairs and lie in the fifth segment of the 
abdomen Betten, 1901 finds the gonads for M. cinerea in segment 
four; Lubben, 1907, records Anabolia nervosa and Limnophilus stigma 
as having the organs in segment five, Rhyacophila septentrionis and 
Brachycentrus montanus in segment four. Klapalek, 1888, gives the 
gonads a general location of segment three, but neither literature nor 
my own observations uphold this statement. From a compilation 
of records the position appears to be in either the fourth or fifth 
segment. 

ALIMENTARY CANAL. 

General description: The alimentary canal, in the order Trichoptera, 
passes as almost a straight tube from buccal cavity to anus. Pictet, 
1834, figures the tube as practically undifferentiated in its shape and 
only varying slightly in size at the extreme ends. Klapalek, 1888, 
states that the regions merge imperceptibly into each other. Although 
this condition may be true in a specimen gorged with food, the writer 
has never seen a specimen where the three main divisions of stomodeum, 
mesenteron and proctodeum were not distinctly marked one from the 
other. The lack of convolutions as are normal in the alimentary canals 
of insects which are herbivorous, is unusual, as Siltala, 1907, shows that 
the order is in the main herbivorous and yet this general type of a 
straight tube prevails. There are a few semi-carnivorous species, but 
even here there is no variation from the above condition. The assimi- 
lative area is increased by an unusual width in proportion to that of 
the body, for in many places and especially the mesenteron, the width 
is equal to one- third and frequently more than one-third the width of 
the abdomen. Another device adds to this area or surface for the wall 
of the mesenteron is folded into transverse ridges which increase the 
surface by three times that actually occupied by the wall, Plate XV, 
Fig. 10. These folds are deeper in the strictly herbivorous types, such 
as L. indivisus, than in those which are more or less carnivorous, as 
H. analis. We will pass now to a discussion of the alimentary canal 
in the three species. Hydropsychodes analis Banks, Plate XV, Figs. 
7, 8 and 9. The surface of the stomodeum of the alimentary canal 
presents a silvery appearance, due to the peritoneal covering of the 
muscles which surround and control the activities of this portion of the 
canal. This portion is much darker than the remainder of the canal, 
due to the food within. If this be cleaned, the wall appears transparent. 
Beneath the peritoneal membrane can be seen the longitudinal muscles 
arranged in pairs in six equi-distant places around the canal. Under- 
neath these longitudinal muscles lie the circular muscles, which are so 



1922] Branch: Internal Anatomy of Trichopter a ''261 

heavy and thick that they give the canal the appearance of having 
great rings around it. The stomodeum is composed of four parts, 
namely: buccal cavity, oesophagus, crop and proventriculus. The buccal 
cavity is large, including half the depth of the head capsule, it narrows 
rapidly and passes over into a slender tube which passes beneath the 
supra-cesophageal ganglia as the oesophagus. The oesophagus extends 
backward through the head and prothorax with only slight expansion. 
At the posterior margin of the prothorax it begins to enlarge and extends 
through the length of the mesothorax with a diameter one-third that 
of the thorax and four times the diameter of the oesophagus in the 
prothorax. This is the crop. At the posterior margin of the meso- 
thorax the stomodeum is suddenly constricted to about half its width 
and within a longitudinal distance of .5 mm. suddenly enlarges to form 
a cylindrical structure, the wall of which becomes resistant to dissecting 
instruments and is very hard. The circular muscles are larger and 
heavier in this region and inside the tube are chitinized teeth. This 
portion is the proventriculus, which functions as a grinding organ 
and possibly as a straining device. 

The cylindrical shape ends suddenly at the posterior margin of the 
metathorax and the transition into the mesenteron is well indicated by 
change in color, texture and structure of the wall and by a deep fold. 
The proventriculus pushes into the forward end of the mesenteron and 
forms there an cesophageal valve. The mesenteron folds up over the 
proventriculus and causes a distinct line to appear between the two 
portions. The silvery tone of the wall is lost at this juncture; the 
longitudinal muscles break up to form a layer of muscles around the 
mesenteron and this layer extends the full length of the mesenteron. 
Beneath these muscles can be seen the very thin layer of circular muscles. 
The mesenteron enlarges at its beginning to at least a third the diameter 
of the abdomen of the larva and increases slightly toward the fourth 
segment and then returns to its width at the beginning before it reaches 
its length. This division arises at the posterior end of the metathorax 
and extends through the length of the abdomen as an almost straight 
tube, varying only as above in diameter, circular in cross section, and 
possessed of an extremely thick wall, but one that is easily torn apart. 
In the sixth segment the mesenteron becomes about two-thirds the 
diameter at its beginning and passes over into the proctodeum. The 
proctodeum is composed of intestine, both large and small, and the 
rectum. The mesenteron pushes into the intestine in much the same 
manner that the proventriculus pushes into the mesenteron, but the 
distance is not as great and the valve formed is not a distinct one in this 
species, although the division between the two main divisions of the 
canal is clearly marked. At the point where these two portions meet, 
the Malpighian tubules, of which there are six, make their appearance 
upon the surface. These tubules are situated upon the lateral and 
ventral faces of the alimentary canal and the dorsal face is void of them ; 
however, the first pair may be easily seen from a dorsal view, each mem- 
ber of this pair lies upon the upper portion of the lateral face and 
extends forward through the abdomen and into the metathorax. Slightly 



262* ''Annals Entomological Society of America [Vol. XV, 

below the first pair, the second pair arises and extends, each member 
of the pair upon its respective side of the alimentary canal, forward 
for the remaining distance of the sixth segment where it turns back- 
ward and taking an upward and lateral direction, with regard to the 
intestine, curves and coils about in the lower part of the abdomen back 
of the sixth segment. The third pair of tubules is situated upon the 
venter about equidistant from each other and from the corresponding 
members of the second pair. This third pair extends backward 
immediately and each member comes to lie beneath and to the side of 
the intestine, intertwining with the corresponding member of the 
second pair. The tubules are irregular in outline, appearing like small 
oval beads strung upon a thread. In general color they are a pale, 
clear yellow, but blotched at irregular intervals with a kidney-brown 
pigment. They weave in and out among the fat bodies and tracehae, 
and into blood sinuses to perform their function of the" removal of 
nitrogenous waste. 

The front end of the intestine is cup-shaped with the larger end 
forward. This portion represents the small intestine. The tube 
grows smaller as it proceeds toward the caudal end. but in the seventh 
segment is greatly constricted; it enlarges immediately and passes 
through segment eight with a diameter of about a fourth that of the 
segment and two-fifths of the diameter of the mesenteron in the first 
segment. This portion represents the large intestine. 

At the posterior margin of segment eight, the intestine is again 
constricted and passes over into the rectum. At this juncture there is a 
semi- valve formed by the invaginated walls of the intestine. These 
folds become longer and fewer in number and form the blood gills which 
lie in the rectum. The rectum extends through the ninth segment. 
In some forms examined, the small diameter of the constricted region 
at the posterior end of segment seven prevails through the eighth, 
widening suddenly at the beginning of the ninth to accommodate the 
invaginations forming the blood gills; in other forms the widening is 
gradual through the eighth and passes over gradually into the rectum 
without any noticeable constriction. The wall of the small intestine 
is heavy and surrounded with circular muscles. It becomes thinner as it 
extends toward the large intestine. When the rectum is reached the 
wall is exceedingly thin and almost transparent. Through the wall 
can be seen the four pockets or invaginations which form the blood gills, 
and into these muscles extend from the lateral and ventral walls at the 
conjunctiva between segments eight and nine. The rectum now serves 
a double function, that of elimination of fecal matter and secondarily 
that of respiration, when oxygen cannot be obtained by means of the 
tracheal gills. These blood gills have no tracheae running into them 
as a glycerine mount of the caudal portion of a fresh specimen clearly 
demonstrates. They function, when the larva is out of the water, by 
protruding themselves through the T-shaped anus, in which state they 
are filled with blood. A detailed account of their structure will be 
found elsewhere in this paper. 



1922] Branch: Internal Anatomy of Trichoptera 263 

Limnophilus indivisus Walker,* Plate XV, Figs. 1, 2, 3 and 5. 
In this form the oesophagus passes from the buccal cavity into the head 
region where it is a small tube and continues through the prothorax. 
The crop is absent in this form and the oesophagus passes immediately 
into the proventriculus. Here the chitinized "teeth" upon the lining 
such as we find in H. analis are lacking. They are not needed, as the 
form is strictly herbivorous and H. analis is semi-carnivorous. The 
oesophagus begins to enlarge at the posterior edge of the prothorax to 
form the proventriculus, which lies in the mesothorax. It is silvery in 
appearance and dark colored, but not resistant to the needle owing 
to the lack of chitinized teeth within. The proventriculus possesses 
the six pairs of longitudinal muscles and the circular layer, but these 
are not as heavy as in H. analis. At the posterior margin of the 
mesothorax the proventriculus constricts slightly and passes over into 
the mesenteron. This position is contrary to the usual division level 
for these two portions of the alimentary canal, but the oesophageal 
valve occurs here and the character of the wall changes to a light pale 
color,, is thicker in cell depth and the six pairs of muscles from the 
proventriculus form the characteristic layer around the new division. 
From these characteristic markings there can be no doubt as to this 
transition. The oesophageal valve is normal, Plate XV, Figs. 2 and 3 
show it as a complete imagination of the wall, in a fold of eight pro- 
jections 

The mesenteron takes its beginning in the mesothorax and increases 
in diameter as it passes through the metathorax. It may be slightly 
constricted in the first abdominal segment although it frequently 
passes without any change of contour. It passes through the abdomen 
at its diameter of one-third that of the abdomen and extends to the 
sixth segment. Here the transition into the intestine occurs and the 
juncture is marked by the presence of the six Malpighian tubules, 
in the same arrangement as in H. analis. The tubes are longer, however, 
and the first pair does not extend into the thorax, but turns backward 
in the first abdominal segment and returns to the seventh. The 
second pair frequently extends as far as segment three and then returns 
to segment eight. The third pair may continue forward through 
segment six before turning backward. The junction between mesenteron 
and intestine is marked by a decided valve not found in H. analis 
and similar to the oesophageal valve. A section showing this structure 
is on Plate XV, Fig. 10. The intestine at its forward end is also cup- 
shaped and, at the constriction between small and large intestine, 
possesses a valve formed by the in vagina tion of the intestinal wall. 
(Plate XV, Fig. 5). Along the intestine are six muscle bundles which 
seem to control the initial position of the Malpighian tubules. Marchal, 
1892, considers the tubules as being capable of motion and perhaps 
these muscles have some part in that action. These muscles likewise 
support the front edge of the rectum into which the large intestine 
telescopes. 

* This species is selected for a comparison with H. analis, as the two rep- 
resent widely divergent forms. 



264 Annals Entomological Society of America [Vol. XV, 



Phryganea interrupta Say* Plate XV, Fig. 11. 

In P. interrupta, the oesophagus passes through the head as a 
narrow tube and enlarges toward the posterior margin of the prothorax 
to form a crop of small dimension which is marked from the proven- 
triculus by a slight constriction. The proventriculus occupies the 
meso and metathorax in length and practically fills the whole of the 
body cavity in this region, it presents the silvery surface as in the 
other forms and the longitudinal and circular muscles are evident. The 
posterior end of the proventriculus extends over into the first abdominal 
segment and here is constricted suddenly and passes through this seg- 
ment as a small tube about one-fourth the diameter of the proventriculus 
in the mesothorax. This constriction is so long that the longitudinal 
muscles of the proventriculus do not follow the tube but span the dis- 
tance from the beginning of the constriction to the surface of the 
mesenteron and can be seen as threads across the open space. f 

The mesenteron is the same as in the other forms and passes over 
into the intestine of the proctodeum in the sixth segment where the 
Malpighian tubules arise. These do not always assume the same posi- 
tions, which is further evidence of Marchal's theory on their mobility. 
Marchal, 1892. The intestine extends through segments six and seven 
and at the anterior margin of the eighth there is a constriction as the 
intestine passes over into the rectum. The rectum gradually grows 
smaller as it nears the anus. The anterior portion of the intestine has a 
heavy musculature and the lower part is ridged longitudinally and these 
ridges become more prominent in the rectum and form four longitudinal 
columns which continue to the anus. 

HISTOLOGY OF THE ALIMENTARY CANAL. J 

In this work the writer has divided the material into two parts: 
that dealing with cellular structure and that relating to the musculature 
of the canal. The condition in H. analis is taken as a basis of compar- 
ison and where L. indimsus differs from the above the condition is noted 
and illustrated in the figures. 

Buccal cavity: The cells are flat and small with small nuclei The 
cavity is heavily lined with chitin. 

* This third species is selected on account of its larger size, 
f A normal cesophageal valve occurs at the division between proventriculus 
and mesenteron. 

J In the histological work, both hot Gilson's and hot Bouin's were used with 
equal advantage if the material was to be used at once. If more than a month 
were to elapse before the material would be used, Bouin's was by far the better 
fixative, as those in Gilson's softened rapidly. 

Much better results were attained by clearing in xylol than in cedar oil. 
An infiltration of not longer than nine hours, including the time in xylol and 
paraffin, equal parts, at 52 degrees F., produced the material most easily cut. 

Staining in Delafield's haemotoxylin and counterstaining in aqueous %% 
eosin produced excellent results as a general stain. For muscles and epithelial 
cells, iron haemotoxylin made clearer slides than the above. Paracarmine with 
a counter stain of orange G. was especially adapted to digestive epithelial tissue in 
L. indivisus. 



1922] Branch: Internal Anatomy of Trichoptera 265 

Oesophagus: The cells of the epithelium are cubical and the whole 
epithelium is lined with a chitinous intima. The basement membrane 
is distinct between the epithelium and the muscles surrounding the 
resophagus. 

Crop: Conditions the same as in the oesophagus. 

Proventriculus : The cells of the epithelium do not vary from those 
of the oesophagus but the wall itself is thrown into folds and the intima 
becomes thick and dense and forms the stomachic teeth, the number of 
which is about thirty-six. A cross section of this region shows them 
surrounding the cavity At the posterior margin of the proventriculus 
is the cesophageal valve which in this form is of peculiar plan. It is 
practically double with a strongly chitinized invagination into the pro- 
ventriculus and an extremely deep but narrow invagination into the 
mesenteron This valve does not completely surround the constriction 
between the two divisions. For further details see Noyes 1915. This 
valve in L. indimsus is normal and complete. It extends into the mesen- 
teron in a fold, the upper part of which is composed of cubical cells with 
an extremely heavy intima, while the under portion of the fold although 
the cells are cubical become somewhat flattened and the intima reduced 
to a thin membrane. The wall changes suddenly into the columnar 
structure of the mesenteron with its striated border. At the point 
where the intima ceases the peritrophic membrane arises. This is sep- 
arated from the epithelial wall of the mesenteron and surrounds the 
food in the canal, Plate XV, Fig. 6. 

Mesenteron: The epithelium here is similar to that at the posterior 
end of the cesophageal valve except that the cells become more col- 
umnar. The conditions in function accord with those described in the 
dragonfly nymph, Needham, 1907, and need no further discussion 
here The wall of the mesenteron is folded as mentioned in the dis- 
cussion of the gross anatomy of the canal to produce more assimilative 
surface and this condition prevails the entire length of the mesenteron 
to the sixth segment. In this same segment the Malpighian tubules 
show upon the surface and the mesenteron passes over into the intestine, 
Plate XV, Fig. 10 at dep. 

Malpighian tubules: At the posterior end of the mesenteron where 
the cells are still columnar, the ventral pair of Malpighian tubules may 
be seen breaking through the epithelial wall on their way to the surface, 
Plate XVI, Fig. 7. Patten, 1884, in his embryological investigation of 
the Trichoptera shows that these tubules are evaginations of the proc- 
todeum before the wall of the forming mesenteron is joined with that 
of the proctodeum. Further evidence of this is seen in sections of the 
intestine further back where the tubules may be seen forming within 
the epithelial tissue of the intestinal walls. The cells are still columnar 
but the presence of intima and the Joss of the striated border indicate 
that this is no longer mesenteron, Plate XVI, Fig. 6. The Malpighian 
tubules are composed of large cells/ glandular in appearance, with a 
large nucleus in the center of the /cell. The pigment so noticeable in 
gross structure now becomes morel evident and stains darker than the 
nucleus and is not confined to a given region of the cell. There are three 



266 Annals Entomological Society of America [Vol. XV, 

distinct layers; upon the inside is the lining or the intima, then the 
large celled wall and the covering which is muscular, Plate XVIII, 
Figs. 7 and 8. The dorso-lateral and lateral tubules reach the surface 
posterior to the ventral pair. 

Intestine: The transition to intestine in H. analis is accomplished 
with a mere constriction and change in cellular structure, but in L. 
indivisus there is a valve formed as the cesophageal valve is formed, but 
reversed in its components, the upper part of the fold is slightly columnar 
in its cellular structure but covered with intima in a thin coat, the intima 
becomes thicker and the cells cubical as the folds turn toward the 
intestinal wall, Plate XV, Fig. 10. At the posterior edge of segment 
seven the cubical wall changes and becomes large celled with large 
nuclei, Plate XVI, Fig. 2. In H. analis this continues to the anterior 
margin of the ninth segment, Plate XVI, Fig. A at 2. At the beginning 
of the ninth segment the epithelial wall changes to a cubical condition 
which changes only as the wall becomes differentiated into the blood 
gills and returns to the cubical condition when this function ceases. 
The whole length of the intestine is thrown into six longitudinal folds 
which begin in the sixth segment, Plate XVI, Fig. 6, and is traceable 
through all the sections to the rectum where the semi-valve occurs 
and the four blood gills arise. The folds do not continue into the rectum. 
In L. indivisus transition in the eighth segment from the cubical celled 
condition to the large celled, which marks the end of the intestine in 
this form, is a distinct rectal valve not different in character or forma- 
tion from the one into the intestine from the mesenteron; the cells of 
the wall of the rectum are large with large nuclei and this condition 
continues to within .5 mm. of the anus. It is possible to consider the 
rectum of H. analis as beginning at this level and the semi-valve as only 
the transition into the blood gills, but the gross anatomical structure 
seems to bear the former interpretation. 

Musculature: The oesophagus is surrounded with bundles of longi- 
tudinal muscles, outside of which is a layer of banded circular muscles 
and outside of these six pairs of longitudinal muscles so noticeable in 
gross structure. At the anterior end of the proventriculus the inside 
layer of longitudinal muscles cease and the proventriculus is imme- 
diately surrounded by circular muscles, (see Noyes 1915), which con- 
tinue as a sheath of varying thickness for the full length of the alimen- 
tary canal as far as the rectum. 

Mesenteron: The six pairs of longitudinal muscles break up into a 
layer of longitudinal muscles, this layer is composed of large bundles 
upon the outside and small ones upon the inside next to the thin cir- 
cular muscles. See Plate XVI, Fig. 7. 

Intestine: At the anterior end of this division where the cells of 
the epithelium are columnar but covered with intima, a heavy circular 
muscle arises pushing some of the longitudinal muscles outside and 
enclosing the smaller ones, Plate XVI, Fig. 6. In a very few sections 
of .008 mm. in thickness this muscular wall is complete, Plate XVI, 
Fig. 5. The inner layer of circular muscles becomes thicker as we 
advance toward the posterior end of the canal and the inner longitudinal 



1922] Branch: Internal Anatomy of Trichoptera 267 

muscles have formed themselves into the characteristic six pairs and 
those pushed to the outside of the outer circular muscles have ceased, 
Plate XVI, Fig. 4. This heavy outer circular muscle comes to an end 
in the seventh segment, leaving the six longitudinal pairs as the exterior 
layer, Plate XVI, Fig. 3. This condition prevails throughout segment 
eight, Plate XVI, Fig. 2, and past the semi- valve into the gill chamber 
of the rectum, Plate XVI, Fig. 1. For a diagram of this musculature, 
see Plate XVI, Fig. A, the levels drawn are numbered as the figures 
which are taken in cross section at these same levels. The musculature 
of L. indivisus does not vary from this description based upon H. 
analis, with the exception that in the mesenteron the longitudinal 
muscles are of a single layer, Plate XVI, Fig. S. The blood gills of 
H. analis rightfully belong to the discussion of the histology of the 
alimentary canal, but their structure is sufficient to claim for them a 
separate division of this paper. 

Blood Gills of Hydropsychodes analis Banks. 

Protruding from the T-shaped anus, Plate XV, Figs. 8 and 9, 
Plate XVII, Fig. 1, are often seen four transparent, greenish, finger-like 
appendages, Plate XIV, Fig. 3. These are protruded beyond the 
limits of the anus when the larva is out of the water crawling upon 
the rocks, or may be artificially protruded by pressure upon the abdomen 
in the caudal region. Pictet, 1834. states that these appendages contain 
tracheae. There are muscles leading into the gills which might be 
mistaken for tracheae if the microscope were not of high magnification. 
Dufour, 1847, figures these gills as appendages from the rectum into the 
body cavity, but without trachea?. This error of Dufour is easily under- 
stood when the larva is dissected, for it is almost, if not quite, impossible 
to open a larva from the dorsal side and not cut into the rectum so 
that these gills float out as though appendages from it. It is only 
when a lateral opening is made that the true internal position is observed. 
Fritz Muller, 1888, does not show any tracheae in the gills and Thienman, 
1903, and Lubben, 1907, represent these as non-tracheae bearing 
structures. In the glycerine mounts of the caudal end of the abdomen 
with the gills protruding from the anus, the tracheal tubes are seen to 
pass down the sides of the body sending branches to the alimentary 
canal and surrounding tissues. Long branches or continuations of the 
main tracheal trunks extend into the anal pro-legs or drag hooks, 
but in no instance does a single tracheole extend to a gill. In neither 
the transverse sections or the longitudinal ones does tracheal structure 
appear. Muscles and blood make up the content of the gill. These 
gills are in direct communication with the body cavity and it is possible 
that, when occasion renders the supply of oxygen insufficient, the blood 
rushes from the blood sinuses into these " pockets" and comes with 
sufficient force and quantity to extend the gill and push it to the exterior 
and an exchange of gases takes place through the wall of the gill. This 
action, combined with the lack of tracheae, seems sufficient evidence 
upon which to claim the term of true blood ^ills for these structures. 



268 Annals Entomological Society of America [Vol. XV, 

When retracted these gills lie within the rectum, which serves a 
double function, with their distal ends or tips close to the anus and just 
barely within the aperture. They may function slightly at this 
time. 

In surface view the gills present a cylindrical form which tapers as it 
extends distally. Upon the surface are transverse ridges which are 
bounded by thread-like depressions. These depressions are as deep as 
the ridges are wide, for these ridges are made up of rings of cells one 
cell deep and one cell wide. At rest these cells are cubical, being as 
deep as they are wide, and the depressions are the expansion spaces 
between the cells. In expansion this ring of cells becomes narrower 
in diameter and the cells themselves wider and more shallow. Compare 
Plate XVII, Fig. 6, where the gill is at rest, and Fig. 7, where it is in 
extended condition. The tips of the gills are more dense and of a darker 
color than the rest of the gill. This condition is due, no doubt, to their 
close proximity to the anal aperture and to the fact that they must at 
times push their way through waste material in their extension. 

To get a clear conception of the formation of these gills, it is necessary 
to start with their origin in the wall of the intestine in the ninth segment. 
Here the glandular large celled condition of the intestinal wall ceases 
and becomes cubical. The wall is thin and the six longitudinal folds 
extend inward so as to form a semi-valve at the head of the rectum, 
Plate XVII, Fig. 4. Gradually these folds merge into four and form the 
four gills. Plate XVII. Fig. 5, shows these longitudinal folds merging 
into the gills and being continuous with them. After the formation 
of the gill the rectal wall does not again fold, but passes directly to 
the anus. 

At rest the width of the gill is about one-third its length, which 
normally is slightly less than the width of the ninth segment. The gill 
is capable of extension to about three times its normal length, and at 
this time the wall becomes thin and the cells much longer than deep. 
Not all of this extension length is made by the gill itself, as the folds at 
the head of the rectum extend and the caudal wall of the rectum itself 
is carried down with the gills, Plate XVII, Fig. 7. 

The deep cells of the walls of the gills are possessed of large nuclei 
and are glandular in appearance. These cells take up about four- 
fifths of the diameter of the gill when at rest, leaving the other fifth 
for the muscle which extends from the conjunctiva of the lateral and 
ventral walls between segments eight and nine. Each gill possesses a 
muscle which arises at a corresponding place upon the conjunctiva 
and extends to the tip of the gill. Each gill muscle is three branched, 
Plate XVII, Fig. 8, and when at rest lines the gill. The gills are covered 
with a very thin intima, which is continuous with that of the rectum 
and intestine. 

GLANDS. 

Not all the glands in the body of the trichopterous larvae are con- 
sidered here. The writer has confined her attention to the silk glands, 
the thoracic glands and the glands in the head, in this last only those in 
L. indivisus have been studied. 



1922] Branch: Internal Anatomy of Trichoptera 269 

The Silk Glands: Of all the glands of the trichopterous larvae 
these are the most prominent. They practically fill the part of the 
body cavity not occupied by the alimentary canal and extend from the 
labial spinneret into the seventh segment. They are opaquely white, 
having a pinkish cast in a fresh specimen. Their content is sticky and 
if the glands of a fresh specimen be broken in dissection the secretion 
will so glue the organs and tissues together as to make further dissection 
impossible. This difficulty is remedied by applying Gilson's preserva- 
tive to the freshly opened specimen and allowing it to remain for fifteen 
or twenty minutes. 

Upon the floor and in the center of the anterior edge of the labium 
is a spinneret, Plate XVIII, Fig. 3, at sp. This is connected to a single 
tube of .2 mm. in length. In this region is the silk press composed of 
muscles which control the flow of secretion. This structure does not 
differ from the structure of the forms studied by Gilson, 1894, and needs 
no further discussion in this paper. At the posterior margin of the 
labium this single, slender tube becomes divided into two and passes 
ventrad of the nerves extending from the sub-cesophageal ganglion to 
the mouth parts. On reaching the ganglion each member of the pair 
of tubes passes laterad of the ganglion, Plate XVIII, Fig. 4, and then 
approaches its mate and passes with it underneath the oesophagus. At 
the posterior margin of the sub-cesophageal ganglion the tubes change 
their character from that of a duct to a true gland. In the duct the 
cells are small with simple nuclei. Externally the change is marked 
with a depression as though a thread were fastened tightly around the 
tube. Back of this depression is the gland proper, composed of an 
outer wall with an irregularly shaped nucleus in a flattened cell. This 
outer wall is two cells in circumference, the cells are hexagonal with 
the lateral face in a triangle. The front face of the triangle meets 
the posterior face of the triangular side of the other cell, see Plate 
XVIII. Fig. 5. Inside of this wall, which is frequently very loosely 
applied, is the inner tube consisting of a firm cylindrical wall, where 
the secretion is formed and inside of this heavy wall is a narrow tube 
through which the secretion passes to the duct, Plate XVIII, Figs. 
6 and 6a. 

These silk glands lie ventrad of the alimentary canal throughout the 
thorax and frequently as far as the second abdominal segment. Finally 
they make their appearance at the sides of the alimentary canal and 
increase in size They extend to the sixth segment where they turn 
forward again and extend to the second and third abdominal segment, 
turning backward they reach to the seventh segment where the distal 
ends are frequently folded under the intestine or float free among the 
various folds of the Malpighian tubules, Plate XV, Fig. 1. For a 
detailed description of these glands see Vorhies, 1908. 

Thoracic glands: Gilson, 1896, shows Phryganea grandis as possess- 
ing three glands or pairs of glands in the thorax, one pair to each of the 
segments. These glands are formed of small tubes which come together 
to form a small reservoir from which a single tube extends. This tube 
meets its fellow and together as one tube they open to the exterior in a 
small pore. Henseval, 1895-6, did not find the three pairs in all of the 



270 Annals Entomological Society of America [Vol. XV, 

forms studied but found a compound gland in the prothorax. This is 
the condition of L. indivisus and P. inter r up ta, although the structure 
of the two glands is not the same. In P. interrupta it resembles the glands 
found by Gilson in P. grandis and is much branched, Plate XVIII, 
Fig. 9, and Plate XIV, Fig. 2, ggl. The gland in L. indivisus is single 
and lies above the prothoracic ganglion, its opening is between the 
connectives of this ganglion to the sub-cesophageal and connects with a 
spinneret which lies at the extreme anterior margin of the prothorax 
and extends forward under the head, Plate XV, Fig. 1, at ggl, Plate 
XVIII, Fig. 1, ggl, and Fig. 10. In H, analis a gland, corresponding 
to this gland of Gilson, has not been found. 

Glands in the Head of Limnophilus indivisus Walker. 

In the head are six pairs of glands exclusive of the silk glands. 
Lucas, 1893, Henseval, 1895, and Russ, 1907, mention two pairs and 
term them mandibular and maxillary glands. L. indivisus possesses 
these two pairs and others. The mandibular gland is situated on the 
outer angle of the mandibular sclerite and is composed of a number of 
single celled glands or " pockets" which open into a common duct. 
This common duct leads to the base of the sclerite, the name of which 
it bears, Plate XVIII, Fig. 14. The maxillary gland, as Lucas so terms 
the second of the head glands, is similar to the mandibular but is com- 
posed of many more of the small single celled glands. The two glands 
lie underneath the oesophagus with their several small lobes folded 
upon each other and their ducts extending almost at right angles from 
each other. These ducts open into the buccal cavity at the inner margin 
of the mandibular sclerite, Plate XVIII, Fig. 13. Patten, 1884, states 
that they are an invagination of the inner margin of the mandibular 
sclerite in the embryo and Patten terms them salivary glands. Further 
ventrad in the lead lies a multicellular gland in the maxillary sclerite 
with an opening into the distal end of this sclerite, Plate XVII, Fig. 12. 
In the labium we find a pair of similar glands, Plate XVIII, Fig. 1 1 . With 
these glands hitherto undescribed, and which we must, from their position 
at least, term maxillary and labial glands, the so-called maxillary glands 
of Lucas present a problem for nomenclature. Lucas ventures the 
theory that the glands of the head are coxal glands and the homologs of 
the parapodal glands of the annelid. If this theory be accepted then 
the maxillary sclerites may not be possessed of two pairs of glands nor 
may the mandibular sclerites. The writer prefers to use Patten's name 
of salivary- gland, for the maxillary gland of Lucas. 

Glands also exist at the base of the antennas and below the visual 
area, but these are not figured. 

Circulatory system of L. indivisus: This is simple as in all insects 
and consists of the dorsal vessel which extends from the ninth segment 
of the abdomen to the head, where it spreads out upon the supra- 
cesophageal ganglia. There are nine pairs of alary muscles beginning 
between the metathoracic and first abdominal segments and continuing 
to lie between the segments as far back as between the eighth and ninth. 
The first four are slender but the remaining five are heavy and connect 
with the one in front and behind it. In front of each pair of muscles, a 
valve exists in the dorsal vessel, Plate XIV, Fig. 8. 



1922] Branch: Internal Anatomy of Trichoptera 271 



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1922] Branch: Internal Anatomy of Trichoptera 273 



EXPLANATION OF PLATES. 

PLATE XIV. 

Fig. 1. Central nervous system of Limnophilus indivisus and larval reproductive 

organs. 
Fig. 2. Central nervous system of Phryganea interrnpta and larval reproductive 

organs gdl=gonad from the ental lateral aspect. gd2 = gonad 

frequently found and assumed to be the ovarian gonad. 
Fig. 3. Central nervous system of Hydropsychodes analis and anal region with 

blood gills protruding from anus. 

Fig. 4. Dorsal aspect of the supracesophageal ganglia of Limnophilus indivisus. 
Fig. 5. Lateral aspect of the supracesophageal and subcesophageal ganglia of 

Limnophilus indivisus. 

Fig. 6. Ventral aspect of subcesophageal ganglion of Limnophilus indivisus. 

Fig. 7. Transverse section through the ovary of H. analis. 

Fig. 8. Ventral aspect of the circulatory system of L. indivisus. 

PLATE XV. 

Fig. 1. Lateral aspect of the alimentary canal of Limnophilus indivisus. 
Fig. 2. Oesophageal valve of Limnophilus indivisus. The portion of the canal 

containing the valve has been slit longitudinally and the valve laid 

open. 

Fig. 3. A transverse cut back of the oesophageal valve. 
Fig. 4. Diagram to show the relative position of the Malpighian tubules at the 

division between mesenteron and hind intestine. 

Fig. 5. Transverse cut through the rectal valve at a level with 5 in Fig. 1. 
Fig. 6. Lateral section through the oesophageal valve. The cephalic end of the 

valve is toward the bottom of the page. 

Fig. 7. Lateral aspect of the alimentary canal of Hydropsychodes analis. 
Fig. 8. Caudal aspect of anus of Hydropsychodes analis. 
Fig. 9. Dorsal aspect of the anus of Hydropsychodes analis. 
Fig. 10. Longitudinal section through the division point between mesenteron 

and hind intestine showing a valve, caudad of the Malpighian tubules; 

and the folded digestive epithelium of the mesenteron. 
Fig. 11. Ventral aspect of the alimentary canal of Phryganea interrupta, only the 

ventral pair of tubules are figured. 

PLATE XVI. 

Fig. A. Diagram of the hind intestine of Hydropsychodes analis, with the levels at 

which the figures 1-6 are taken, indicated. 
Fig. 1. Cross-section through the hind intestine at a point where a semi-rectal 

valve is formed by the invaginated folds of the intestinal wall. 
Fig. 2. Cross section taken at level No. 2, showing the glandular structure of 

the large intestine. 
Fig. 3. Cross section at level Xo. 3, showing the six folds of the small intestine 

with the cubical cell in the wall and the ental layer of circular 

muscles with the six pairs of longitudinal muscles. 
Fig. 4. Cross section at level No. 4. showing the ectal row of circular muscles 

in addition to the condition in Fig. 3. 
Fig. 5. Cross section at level No. 5, showing the beginning of the columnar 

epithelial cells and the breaking up of the six pairs of longitudinal 

muscles into a layer of smaller longitudinal muscles. 



274 Annals Entomological Society of America [Vol. XV, 

Fig. 6. Cross section at level No. 6, showing the Malpighian tubules forming 
in the hind intestine; also the breaking up of the ectal circular muscles. 
Note the presence of intima which indicates the structure as being a 
part of the hind intestine. 

Fig. 7. A cross section slightly cephalad of the level of Fig. 6, showing the 
digestive epithelium in diagram and the heavy layer of longitudinal 
muscles characteristic of the mesenteron. The ventral pair of 
Malpighian tubules are seen here just coming to the surface. 

Fig. 8. A portion of a cross section of the mesenteron of Limnophilus indivisus, 
which shows the normal two row r s of muscles. 

PLATE XVII. 

Blood Gills of Hydropsy chodes analis. 

Fig. 1. Cross section of anal region to show the T-shaped anus. X 70. 
Fig. 2. Cross section through the anus with a gill lying in the aperture. X 70. 
Fig. 3. Cross section through the rectum showing all four gills. X 70. 
Fig. 4. Cross section through the "so-called rectal valve." X 140. 
Fig. 5. Sagittal section of the gill region showing the intestinal wall invagina- 
tions that make the valve as at Fig. 4, and later make the gill wall 
itself and are continuous with the rectal wall caudad of the gills. 
Fig. 6. Sagittal section of the gill region to show the retractile muscle of the 

gill and the relation to the body wall. 
Fig. 7. Sagittal section of the gill region with the blood gills extended in 

function. X 125. 

Cross section of a functioning gill showing the three muscle branches. 
The blood which fills the gills when in function. X 320. 

PLATE XVIII. 

Fig. 1. Dorsal view of the silk glands and Gilson's gland of L. indivisus. 
Fig. 2. Ventral view of the mouth parts of L. indivisus with the silk glands 

located. 

Fig. 3. Lateral aspect of the mouth parts of L. indivisus. 
Fig. 4. Dorsal aspect of the silk glands in relation to the suboesophageal 

ganglion. 

Fig. 5. Lateral aspect of a portion of the silk gland. 
Fig. 6. Cross section of the gland proper of the silk gland of H. analis. 
Fig. 6a. Cross section of the gland proper of the silk gland of L. indivisus. 
Fig. 7. Longitudinal section of a Malpighian tubule. 
Fig. 8. Cross section of a Malpighian tubule. 

Fig. 9. Dorsal aspect of the Gilson's gland of P. inter rupta in relation to the 
prothoracic ganglion. 

Fig. 10. Dorsal aspect of the Gilson's gland of L. indivisus in relation to the 

prothoracic ganglion. 

Fig. 11. Ventral aspect of the glands in the labial sclerite of L. indivisus. X 120. 
Fig. 12. Ventral aspect of the gland in a maxillary sclerite of L. indivisus. X 120. 
Fig. 13. Ventral aspect of the maxillary gland of Henseval and Lucas. X 30. 
Fig. 14. Ventral aspect of the mandibular gland. X 30. 
Fig. 15. Cross section of several of the unicellular portions of the maxillarv eland 

of Henseval and Lucas. X 30. 



1922J 



Branch: Internal Anatomy of Trichoptera 



275 



INDEX TO FIGURES. 



a = anus. 

abg = abdominal ganglia 1 to 8. 

abs = abdominal segment 1 to 9. 

ant = antennal nerve. 

af = alary muscle 1 to 9. 

b= nerve to front .of head. 

bc = buccal cavity. 

bg = blood gills. 

bm = basement membrane. 

c = crura cerebri. 

cr = crop. 

cm = circular muscles. 

cp = corpuscle. 

ct = conducting tubule. 

dep = digestive epithelium. 

dh = drag hooks. 

dv= dorsal vessel. 

ep = epithelium. 

ex = expansion area. 

excm = exterior circular muscle. 

fa=frontal arm. 

fg= frontal ganglion. 

gd = gonad. 

gdl=gonad in inner aspect. 

gd2 = probable ovary of P. interrupta. 

ggl = Gilson's gland. 

glep= glandular epithelium. 

gsp = spinneret of Gilson's gland. 

in = intima. 

1 = Lumen. 

Itrl = labral nerve. 

Ib2 = labral nerve. 

lb-s = labral sclerite. 

111 = labial nerve. 

112 = labial nerve. 
li-s = labial sclerite. 
l-int = large intestine. 
1m = longitudinal muscle. 
md2 = mandibular nerve. 



md-s = mandibular sclerite. 

me = mesenteron. 

mp = Malpighian tubule. 

mpl = dorso-lateral pair. 

mp2 = lateral pair. 

mp3 = ventral pair. 

ms = mesothorax. 

mstg = mesothoracic ganglion. 

mt=metathorax. 

mttg = metathoracic ganglion. 

n = nucleus. 

oe = oesophagus. 

og = opening of gland. 

opt = optic nerve. 

oev = oesophageal valve. 

or=oesophageal ring. 

p = pigment. 

pm = gills press muscles. 

pr = proventriculus. 

pro = prothorax. 

protg = prothoracic ganglion. 

ptm = perotrophic membrane. 

r = rectum. 

rm = retractile muscle. 

rn = recurrent nerve. 

rv = rectal valve. 

rw = rectal wall. 

s = sympathetic ganglion. 

sb-oeg = sub-oesophageal ganglion. 

spr-oeg = supra-oesophageal ganglion. 

skc = silk gland duct. 

skp = silk gland proper. 

sb = striated border. 

sm-int = small intestine. 

sp = spinneret. 

t = tubule. 

tr = trachea. 

y = ventral end ot ovary. 



ANNALS E. S. A. 



VOL. XV, PLATE XIV. 




HEB. 



Hazel Elisabeth Branch. 



ANNALS E. S. A. 



VOL. XV, PLATE XV. 




Hazel Elisabeth Branch. 



ANNALS E. S. A. 



VOL. XV, PLATK X\\. 




mp 3 



Hazel Elisabeth Branch. 



H. E. B. 



ANNALS E. S. A. 



VOL. XV, PLATE XVII. 




H. E. B. 



Hazel Elisabeth Branch. 



ANNALS E. S. A. 



VOL. XV, PLATE XVIII. 




H.EB. 



Hazel Elisabeth Branch. 



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PGICAI, SOCIETY 
tanaging Editor, 



Syracuse, N. Y. 

PAT. JAN 21, 1903 



507/55 



BJOLOY 
LIBRARY 



UNIVERSITY OF CALIFORNIA LIBRARY 



